The present invention relates to a pressurized fluidized bed. Heated air flows through the pressurized container of a known fluidized bed burner that can operate either in the atmosphere or under pressure (1984 Technical Bulletin, pp. 304-06) and arrives in the bed through an air box. The wall of the pressurized container is exposed to heat from the heated air and must be designed to withstand the stress. Whereas the thermal stress is comparatively slight when the device is operated in the atmosphere, the wall of a container that is operated under pressure must be fairly thick, which considerably increases the weight of the container. Attempts have been made to avoid the problem in this known fluidized bed burner by diverting the preliminary air heater through a bypass line. The air is accordingly heated in the preliminary heater only in atmospheric operation. Although lost heat is usually exploited to practical purpose in a preliminary air heater, that advantage is lost when the heater is diverted.
The pilot burners that start another known fluidized bed burner (VDI Report 322 [1978], 89) are positioned near the air box and inside the pressurized container. Pilot burners located there, however, are hard to access and tend to get clogged up.